Process for producing nitrosocyclohexane dimer



ABSTRACT OF THE DISCLQSURE A process for producing nitrosocyclohexane dimer which comprises the steps of pyrolyzing in the presence of nitrogen monoxide at least one cyclohexylcarbinol nitrous acid ester at a temperature of 250 C.600 C. under a pressure of from 0.5 to 0.002 atmosphere.

This invention relates to a new process for producing nitrosocyclohexane dimer. More particularly, the inven tion relates to a process for producing nitrosocyclohexane dimer by the pyrolysis of the carbinol nitrous acid esters having a cyclohexyl radical, which is represented by the formula wherein is the cyclohexyl radical and R and R are hydrogen or a primary alkyl radical having 1-4 carbon atoms and may be the same or different. For convenience sake, the starting material in the present invention, as represented by the foregoing formula, will be hereinafter referred to as cyclohexylcarbinol nitrous acid esters. The nitrosocyclohexane dimer is readily rearranged to cyclohexanone oxime by heating and, in turn, this can be made into e-caprolactam by the Beckmann rearrangement reaction. Hence, the nitrosocyclohexane dimer is an important in termediate for the production of e-caprolactarn, which forms polycaprolactam on polymerisation.

The nitrosocyclohexane dimer has been synthesized in the past by various processes. For example, as processes for its production, known are such as the oxidation of cyclohexylamine, the oxidation of cyclohexylhydroxylamine and the photochemical reaction of cyclohexane and nitrosyl chloride.

The present invention, however, diflering entirely from these conventional processes as to its form of reaction, is a new process for the production of the nitrosocyclohexane dimer.

According to the invention process, the aldehydes or ketones can be formed besides the intended nitrosocyclohexane dimer.

This invention is directed to a process for producing nited States Patent U the nitrosocyclohexane dimer by the pyrolysis of the cyclohexylcarbinol nitrous acid esters having the formula wherein Thus, it is believed that the cyclohexyl radical formed in the decomposition of alkoxy-radical (2) bonds with NO formed in the primary decomposition 1) to become nitrosocyclohexane by reaction (3), which subsequently can be transformed into the nitrosocyclohexane dimer by reaction (4). That the products obtained by the thermal decomposition are the nitrosocyclohexane dimer and aldehydes or ketones is explained by the reactions (1) to (4). In the invention reaction, a small amount of nitrogen monoxide and cyclohexylcarbinol are also obtained. The cyclohexylcarbinol obtained as a by-product can be recovered and made into cyclohexylcarbinol nitrous acid esters to be then used again as the starting material by recycling to the system.

As the starting material substance to be used in the invention, any of the cyclohexylcarbinol nitrous acid esters of the formula wherein R and R are as previously indicated, can be used. Included are, for example, such as the cyclohexylcarbinol nitrous acid esters; the cyclohexylmonoalkylcarbinol nitrous acid esters such as cyclohexylmonomethylcarbinol nitrous acid ester, cyclohexylmonoethylcarbinol nitrous acid ester, cyclohexylmono-n-propylcarbinol nitrous acid ester and cyclohexylmono-n-butylcarbinol nitrous acid ester; and the cyclohexyldialkylcarbinol nitrous acid esters such as cyclohexyldimethylcarbinol nitrous acid ester, cyclohexyldiethylcarbinol nitrous acid ester, cyclohexyldin-propylcarbinol nitrous acid ester, cyclohexylmethylethylcarbinol nitrous acid ester, cyclohexylethyl n-propyl carbinol nitrous acid ester and cyclohexyl n-propyl nbutylcarbinol nitrous acid ester.

The invention process can be carried out at a reaction temperature of 2004000 C., and preferably 250600 C., and a reaction tube entrance pressure of 1-0.001 atmosphere, and preferably 0.50.002 atmosphere.

Although the contact time of the starting material, i.e., the dwell time in the system, of 0.01-500 seconds or even more will do, normally a time of 0.05-200 seconds is preferred. The contact time should be chosen in consideration of various factors to ensure that the pyrolytic reaction is carried out suitably.

The invention reaction must be carried out under at least an inert atmosphere. An inert atmosphere, as used herein, refers to one in which there is not present in the reaction system a substance which will either oxidize the starting material used in the invention or capture the cyclohexyl radicals formed under the reaction conditions of the present invention. For rendering the atmosphere of the reaction system of the invention inert, this can be accomplished by replacing the air in the reaction system preliminarily with an inert diluent such as nitrogen or carbon dioxide.

It is preferred to carry out the invention reaction in the presence of nitrogen monoxide, as it is possible to enhance the selectivity of the intended nitrosocyclohexane dimer. As is apparent from the hereinbefore given Equation 3, nitrogen monoxide is a substance which acts as a reactant in the present invention. The NO radicals are formed in the reaction system according to this invention by the thermal decomposition of the starting material cyclohexycarbinol nitrous acid ester. Aside from this however, by efitecting the reaction in the presence of nitrogen monoxide, the NO radicals become excessive and, as a result, the reaction proceeds smoothly to enhance the selectivity of the intended nitrosocyclohexane dimer.

Further, according to the invention, the pyrolytic reaction can be carried out by diluting the starting material' nitrous acid esters and/ or the foregoing nitrogen monoxide with the aforementioned inert diluents. In this case, the nitrous acid ester to be fed and nitrogen monoxide may be diluted in advance with said inert diluent and then fed to the reaction system. The diluent may, of course, also be introduced into the reaction system intermittently or continuously during the reaction. When using the nitrogen monoxide and/ or inert diluent in this invention in this manner, their proportion is preferably within the following range:

Number of moles of nitrogen monoxide Number of moles of the starting material cyclohexylcarbinol nitrous acid ester Number of moles of the inert diluent 0'1 5O Number of moles of the starting material cyclohexylcarbinol nitrous acid ester diluent. It is possible to raise the selectivity of the in: tended nitrosocyclohexane dimer markedly by carrying out the reaction particularly in the presence of nitrogen monoxide and an inert organic solvent. As such inert organic solvents, included are, for example, the aliphatic compounds such as methane and ethane; the alicyclic compounds such as cyclohexane and cyclopentane; and the aromatic compounds such as benzene, toluene and chlorobenzene. The inert organic solvents are preferably used in the following proportion:

In addition, when, of the aforementioned starting material having the formula R and R are as hereinbefore indicated, one is used in the invention in which at least one of either R or R is especially an alkyl radical having 1-4 carbon atoms, the selectivity of the intended nitrosoyclohexane dimer is enhanced.

Thus, a much greater enhancement in the selectivity of the resulting dimer can be had in this invention by suitably combining the hereinbefore mentioned desirable conditions.

Since the pyrolytic reaction of the cyclohexylcarbinoli nitrous acid esters in this invention is an endothermic reaction, desirably used for the reaction tube is one having the best possible heat exchange rate, preferably being either glass or quartz, or the use of a metallic or ceramic packing, or a reaction tube which contains a plate-shaped heat exchanger. g

In general, the cyclohexylcarbinol nitrous acid estersf are unstable to heat and light, and since they tend to decompose to alkoxy radicals, it is preferred that preventive measures be taken to ensure that the foregoing nitrous acid esters are not exposed to such conditions prior to the reaction.

Further, since the formed nitrosocyclohexane dimer easily reacts with the cyclohexylcarbinol nitrous acid esters, it is preferred that the two be promptly separated after the invention reaction.

For a still clearer understanding of the invention, the following examples are given, it being understood that these examples are for illustrating the invention and not in limitation thereof.

wherein Examples 1-9 When the cyclohexylcarbinol nitrous acid esters indicated in column 2 of the following Table I were pyrolyzed by introducing the same in their gaseous state into pyrolytic reaction tubes having the temperatures shown in column 4 and reaction tube entrance pressures shown in column 6 for the contact times indicated in column 5 under the flow of substances shown in column 3, white crystals were obtained in each instance. The white crystals were severally recrystallized from cyclohexane to obtain crystals having the melting points severally of 113.5- l15.5 C. (literature value 116-1165 C.). It was confirmed from infrared absorption sepectra that they were nitrosocyclohexane dimer: v 1200 cm. (VS).

The rates of conversion and selectivity are shown in columns 7 and 8, respectively.

TABLE I Reaction Conditions Substance Added (mole ratio based Conversion, Selectivity, Example Starting Material on starting material) Contact percent percent Temp., Time, Pressure, C. see. mm. Hg

1 Cyctlohexanomethanolnitrousacid None 370 26.0 2.0 59.7 33.9

es er. 2 do Nitrogen monoxide (12.2) 370 129 8 88.2 75.2 3. do Nitrogen monoxide (1. 9) plus cyclo- 370 0.16 7 63. 5 81. 6

' hexane (0.687). 4 Cyclohexylmethylcarbinol nitrous None 370 26.0 7 57.0 45. 8

acid ester. 5 Nitrogen monoxide (5.0) 350 4. 94 14 61.7 87.0 Nitrogen monoxide (2.0) plus cyclo- 380 0.13 6 53. 90.0

hexane (0.731). 7 Cyclohexyldimethylcarbinol None 370 2a 7 32.1 44.7

nitrous acid ester. 8 do Nitrogen monoxide (2.6) 380 0.13 7 92.2 82. 9 -do Nitrogen monoxide (2.6) plus cyclo- 380 0.13 7 72.0 84. 0

hexane (0.814).

It is apparent from the foregoing results, that an improvement is had in the selectivity when the cyclohexylmethylcarbinol or cyclohexyldimethylcarbinol nitrous acid ester having the methyl or dimethyl substituent is used as the stanting ma'terial instead of cyclohexanemethanol nitrous acid ester. This can be seen by comparison of Examples 1, 4 and 7. Further, as is apparent by a comparison of Examples 1, 4 and 7 with Examples 2, 5 and 8 it can be seen that a marked enhancement of the selectivity is had when nitrogen monoxide is present as compared with the instances of its absence; and further 0 in the following Table in.

Examples 14-17 Pyrolyses were carried out as in Examples 19, varying the R and R of the formula with alkyl radicals having 1-4 carbon atoms, 'as indicated The results obtained are shown in said table.

TABLE III Starting Material Reaction Conditions Conversion, Selectivity, Ex. percent percent R R2 Pressure, Tempera- Contact N 0 (mole) mm. Hg ture, C. Time, sec. material(mo1e) CH CH3 6. 0 310 12. 5 1. 4 29. 3 88. 0 CH3 C2H5- 3.0 350 6. 5 6. 7 73. 7 87. 7 16 C H C2H 12. 1 363 2. 05 5. 8 92. 2 82. 5 17. C H C H9 9. 0 400 5. 5 2. 4 71. 0 85. 2

that a still further improvement in the selectivity is had by the conjoint use of an inert organic solvent with the nitrogen monoxide, as shown by Examples 3, '6 and 9. Thus, it is seen that it is desirable in this invention to carry out the pyrolysis using, as the starting material, an alkyl-substituted, and particularly a methyl-substituted, cyclohexylcarbinol nitrous acid ester, in the presence of nitrogen monoxide (and an inert organic solvent), since the selectivity of the nitrosocyclohexane dimer is enhanced.

Examples 10-13 The reactions were carried out following the procedures as described in Examples 1-9, varying the R of the formula Examples 1821 R with methyl, ethyl, propyl and butyl, with the results shown in Table H.

TABLE II Reaction Conditions Example Starting Material Conversion, Selectivity,

Pressure, Tempera- Contact NO (mole) percent percent mm. Hg ture, C. Time, material (mole) see.

Cyclohexylmethylcarbinol nitrous acid ester 24. 0 330 1. 86 1. 4 29. 7 90.0 Cyclohexylethylcarbinol nitrous acid ester- 23. 0 350 9. 5 1. 56 50. 9 82. 3 Cyelohexylpropylcarbinol nitrous acid ester. 14. 0 350 7. 3 5.0 61. 7 87. 0 Cyclohexylbutylcarbiuol nitrous acid ester 48 370 16. 1 2. 4 47. 8 75. 6

were carried out as in Examples 1-9. The results oh- 3. A process for producing nitrosocyclohexane dimer tamed are shown in Table N. which comprises pyrolyzing in the presence of nitrogen TABLE IV Reaction Conditions Inert Inert. Con- Selec- Ex. Starting Material Organic Pressure, Contact NO Orgamc N2 version, tivity, Solvent mm. Tempera- Time, M solvent 2% percent percent Hg ture, C. see. Material QL i Material (mole) Material (mole) (mole) 18".. Cyclohexanemethanol Methane 6.5 370 0.061 0.822 0.698 28.6 73.1

nitrous acid ester. 19 do Chlorobenzene. 14 350 0.7 2.4 0.81 16.8 30.5 71.8 20 1 Cyclohexylnlethylcarbinol Cyclopentaue 4.5 370 0.0774 0.67 0.54 49.3 90.8

nitrous acid ester. 21 do Benzene 6 370 0.17 2.6 1.43 43.5 8 5.0

Examples 22-28 monoxide at least one cyclohexylcarbinol nitrous acid The nitrosocyclohexane dimer was obtained by opester represented byt'he formula crating as in Examples 19 while using the starting 20 R1 materials indicated in column 2 of the following Table I o-oNo V and varying the conditions diversely as indicated therein. The conversion and selectivity rates thereby obtained are shown in the same Table V. wherein TABLE V Inert Gas Inert Organic m NO (mole) (mole) Solvent COFWQY' 1 Ex. Starting Material Temp era- Pressure, Time, W m (mole) sion, tlvity, ture, 0. mm. Hg sec. (mole) (mole) W percent percent (mole) Celoheyxylmethylcarbinolnitrous 200 760 360 Helium 50 95,7 19 7 acid ester. 350 14 7.3 5.0 61.7 87.0 Cyclohexyldimethylcarbinol 370 3 372 1. 98 88 76. 2

nitrous acid ester. Cyclghexyhnethylcarbinolnitrous 370 16.5 69 Nitrogen 18.3.. 66 48.3

aci ester. Cyelohexylpropylbutylcarbinol 400 9 5.5 2.4 71 85.2

nitrous acid ester. Cyelohexylmethylearbinolnitrous 450 2 85 2.93 -1 79.7 85.1

acid ester. (lo 550 5 0.614 2.5 Cyclohexane2.04 91.5 80.1

What is claimed is: 1. A process for producing nitrosocyclohexane dimer {IO- which comprises pyrolyzing in the presence of nitrogen monoxide at least one cyclohexylcarbinol nitrous acid ester represented by t e f r is a cyclohexyl radical, R and R are members se- Rl lected from the group consisting of hydrogen and the alkyl radicals having one to four carbon atoms wherein R and R may be the same or difierent radi- Ri cals but when either R or R is hydrogen, the other h i is an alkyl radical having one to four carbonations, at a temperature of 250 C.-600 C. under a reduced pressure of from 0.5 to 0.002 atmospheres.

4. A process according to claim 3 wherein said pyroly is a cycloheXyl radical, R and R ar m m sis is effected in the presence of an inert organic solvent. leeted from the group consisting of hydrogen and the alkyl radicals having one to four carbon atoms References Cited Whefem 1 and R2 may be the Same or dlfierent 60 Gowenlock et al., J. Chem. Soc. (London), Volume of radlcals, o 1956, pp. 1670-1675.

at a temperature of 250 C.600 C. under a reduced pressure of from 0.5 to 0.002 atmospheres. CHARLES R PARKER, Primary Examinen 2. A process according to claim 1 wherein said pyrolysis is effected in the presence of an inert organic solvent. F. D. HIGEL, Assistant Exammer, 

1. A PROCESS FOR PRODUCING NITROSOCYCLOHEXANE DIMER WHICH COMPRISES PYROLYZING IN THE PRESENCE OF NITROGEN MONOXIDE AT LEAST ONE CYCLOHEXYLCARBINOL NITROUS ACID ESTER REPRESENTED BY THE FORMULA 